MAX11800_1010 Datasheet, PDF(21/59 Page) Maxim Integrated Products – Low-Power, Ultra-Small Resistive Touch-Screen Controllers with I2C/SPI Interface

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MAX11800_1010 Datasheet, PDF (21/59 Pages) Maxim Integrated Products – Low-Power, Ultra-Small Resistive Touch-Screen Controllers with I2C/SPI Interface

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Low-Power, Ultra-Small Resistive Touch-Screen

Controllers with I2C/SPI Interface

the timing of the decision are configurable through the

touch-detect pullup timing configuration register (0x07).

Program the MAX11800âMAX11803 in the context of

the application to maximize power efficiency and

achieve the desired scan throughput.

PUR and PUF

PUR is a fast pullup mode, which uses the main X+

switch in parallel with the resistive pullup to quickly slew

the panel capacitance. PUF uses only the touch-detect

pullup resistor, RTD. PUR and PUF serve the same func-

tion as TDM, but are timed so that the panel can settle

after completing measurements and before rendering

any decisions on the touch status of the panel.

Use the optional PUR mode to reduce the time to tag

data by momentarily placing the panel in a low-imped-

ance (< 10Î©) pullup mode instead of using the avail-

able 50kÎ©/100kÎ© touch-detection pullup resistors. This

operation forces the monitored TSC input high during

the PUR interval. Once the PUR interval expires, a PUF

interval must be allowed so that the panel can recover

and pull the TSC input low in case a touch is present.

The purpose of the PUR mode is to reduce the time

required to determine touch status by avoiding long

pullup time constants caused by high-capacitance

touch panels and the high-impedance on-chip pullup

resistors (RTD). When a touch is present during PUR

intervals, the current through the low-impedance pullup

(XPSW) and panel combination is significantly higher

than that observed in the PUF mode. The durations in

Y+

X-

VDD

PSW

TDRSEL

XPSW

X+

RTD

PUR TSW

RTD

TOUCH

(TO MAX11800/

MAX11801 LOGIC)

PUR, PUF, TDM

PANEL

Y-

YMSW

PUR, PUF, TDM

Figure 6. Touch-Detection Circuitry

MAX11800â

MAX11803

the PUR mode should be matched to the panel charac-

teristics and the desired scan throughput rates to mini-

mize power dissipation.

While use of the PUR mode is optional, the PUF period

is required for all applications. The PUF interval allows

the panel to resettle following scan or optional PUR

intervals. When a touch is not present, the panel capac-

itance settles toward VDD through the internal pullup

switch and a portion of the panel resistance (with the

optional PUR mode disabled). When a touch is present,

the panel capacitance settles toward ground through a

portion of the panel resistance, ideally significantly

lower than the selected pullup impedance, RTD. Allow

enough recovery time for settling through the panel

resistance when using a PUR mode. Figure 7 illustrates

the touch-detection operations.

Idle Modes

Once the PUF period expires, the preceding measure-

ment data is tagged and made available for readback.

The MAX11800âMAX11803 transition to an appropriate

mode depending on the conversion and interrupt mode

selected.

Features Available in the

MAX11800âMAX11803 Averaging Modes

The MAX11800âMAX11803 contain a programmable

averaging filter. When enabled, this feature allows col-

lecting 4, 8, or 16 consecutive samples for each mea-

surement type requested. The number of the samples

for each measurement type is controlled by configura-

tion register 0x03. Averaging can be assigned to each

measurement type. For example, X and Y measure-

ments can use an average of 16 samples, while Z mea-

surements can use one or four samples to save power.

The AUX depth is selected in configuration register

0x0A.

The MAX11800âMAX11803 can be configured to per-

form one of two statistical operations. One option is a

median averaging filter (MAF). The MAF first removes

the lowest and highest values before averaging the

remaining sample set. The second filter type is a

straight averaging filter (SAF), which takes the average

of the entire sample set. Both filter types and

position/pressure averaging are controlled by configu-

ration register 0x0B. Table 4 presents the details of the

median averaging operations of the MAX11800â

MAX11803. For the MAX11800/MAX11801, averaging is

supported in both direct conversion mode and

autonomous conversion mode. The MAX11802/

MAX11803 support only direct conversion mode.

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